EDGE EFFECTS

EDGE EFFECTS
Robert C. McColloch
aka Hortense
January 30, 2006

This forum has been discussing Stand Development and Edge Effects. There’s another way to get to this destination. It’s the use of a Contrast Increase Mask. This is also called an Unsharp Mask a mask that puts you in control of the process. Ok, it’s just another way but this should be worth adding to your library. It’s a process that uses light from multiple angles. It’s a process that uses dilute developer for purposes of acutance. This processes leaves sufficient grains of silver halide intact so that “acutance” is achieved.

This mask among other benefits will provide the degree of edge sharpness that you may wish to achieve on your negative. It will also reduce the need for highlight burning. I probably use an unsharp mask (USM) for about 60 to 70 percent of my 4x5 negatives. This mask controls the degree of a.) edge sharpness and b.) local contrast effectively reducing the amount of burning (the only two reasons to use this method). More explanation later.

The Procedure

No light in the darkroom not even red lights so tape over any red lighted switches.
1. Punch the original negative and mask negative emulsion side up.
2. Place a “witness” mark the vertical enlarger column for an 11x14[/INDENT]print.
3. Put the negative carrier in the enlarger without a negative.
4. Place a 10 ½ inch turntable (e.g., a Lazy Susan) on the enlarger baseboard as far off-axis as possible (i.e., in the corner of the area illuminated by the enlarger light).
5. Using the original negative and the unexposed mask film; make a “sandwich” with the mask film on the bottom and the original on top; both emulsion sides facing down. One at a time, place the punched holes in the film on the diffusion easel base pins thus positioning the sandwich for exposure[/INDENT].
6. Expose the “sandwich” while rotating the turntable . Run about three test negatives to determine best exposure.
For the ASA 125 mask film and the TPX 320 that I use, my exposure ranges in the area of approximately 8-seconds @f/32.
7. From a water soak, develop the mask in the “Slosher” emulsion up.
(Equipment, item e.). Develop in a 1.7% solution of HC110 for precisely 2 ½-minutes while gently rocking; agitate vigorously for 5-seconds
every30-seconds. Complete the process with a stop bath, fixer and HCA.[/INDENT]Note: Dictate a tape with the timing points needed to get you at least to the fixer bath. See Equipment item f.
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A good mask should produce a faint positive image with details that extend only into the middle values of the image. No need to use a densitometer as some advocates claim. In the long run, you can save time by making two masks: One as described above and another using a stronger 1.56% HC110 solution of developer (this stronger solution increases the densities of the mask). Compared to your straight print, a good mask will kick the contrast up at least one grade (maybe two). Therefore a negative that would be a good candidate for unsharp masking (USM) would not print higher than a grade3 ½ or 4.

Edge Effects

The negative sandwich spacing is what determines the degree of edge effect. The more space separating the negative and the mask, the greater the edge effect; simple as that. How is this done? The thickness of original negative’s film base usually provides sufficient separation. If not, sandwich a thin piece of Mylar between the two films. Using TPX320, I find Kodak’s film base to be thick enough to obtain the edge effect I normally desire

Contrast Control

Contrast control is a function of developer concentration. Weak solution, lower contrast. Stronger solution; more contrast. This is why I suggested a 1.70% HC110 solution as a second test negative vs. the 1.56% HC110 solution.

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Remember … for more edge effect
increase the space in the “sandwich”
The best mask produces a faint positive image with details
that extend only into the midtones

By Claire Senft - 09:15 PM, 01-31-2006 Rating: None
This is a nice article Hortense. I have a disagreement with your terminology. A positive image from a mask when combined with a negative will reduce the contrast of the sandwhich requiring the use of a higher grade paper to restore contrast. Therefore the unsharp mask is a contrast reducing mask not a contrast increasing mask. If one would make a print with and without the mask on the same paper grade the contrast will be reduced. To make a contrast increasing mask one would need to combine a negative mask with a negative or a positive mask with a positive. Good luck with your masking.

By hortense - 05:02 AM, 02-01-2006 Rating: None
I did not sufficiently explain the context to this reference. Using an USM it will increase your need to PRINT on a high grade setting. Typically you want a 1-grade increase (or more depending on what you are seeking. Thank for pointing out need for better clarification.

By Daniel Lawton - 01:18 AM, 02-03-2006 Rating: None
Thanks for contributing a very useful article. I tried USM this summer with varying degrees of success but this makes me want to give it another go.

Mike Kriss, author of an extensive article on edge effects has given me permission to publish parts of his work, as applicable on APUG. As soon as I can get around to it, I will scan and upload this work. It was published by the SPSE and ICPS several years ago.